Inorganic light emitting diodes (LEDs) have features of self-luminous, high brightness and so on, and therefore have been widely applied in the fields of illumination, display, projector and so forth. Taking monolithic full color micro-LED displays as an example, monolithic micro-displays have been widely used in projector and faced with a bottleneck of colorizing technology. Generally, in order to obtain different colored lights, epitaxial processes for fabricating a single LED chip including a plurality of light emitting layers capable of emitting different colored lights has already been proposed. In this case, the single LED chip can provide different colored lights. Since lattice constants of the light emitting layers capable of emitting different colored lights are different, growth of the light emitting layers on a same substrate is difficult to be achieved. Accordingly, another solution has been proposed. In order to obtain different colored lights, at least one LED chip capable of emitting light with short wavelength and a plurality of wavelength conversion materials are used, wherein the wavelength conversion materials are capable of being excited by the light emitted from the LED chip and generate excited light having different color. However, the conversion efficiency of the wavelength conversion materials is low and it is difficult to coat the wavelength conversion materials uniformly.
The picking-up and placement technique for LED chips has a better chance to enhance brightness and display quality of a monolithic micro-display significantly. To one ordinary skilled in the art, how to efficiently pick-up and place the LED chips to a circuit substrate of the monolithic micro-display is an important issue.